Well-established power distribution systems exist throughout most of the United States, and other countries, that provide power to customers via power lines. With some modification, the infrastructure of the existing power distribution systems can be used to provide data communication in addition to power delivery, thereby forming a power distribution communication system. In other words, existing power lines that already have been run to many homes and offices can be used to carry data signals to and from the homes and offices. These data signals are communicated on and off the power lines at various points in the power distribution communication system, such as, for example, near homes, offices, Internet service providers, and the like.
While the concept may sound simple, there are many challenges to overcome in order to use power lines for data communication. Power distribution systems include numerous sections, which transmit power at different voltages. The transition from one section to another typically is accomplished with a transformer. The sections of the power line distribution system that are connected to the customers typically are low voltage (LV) sections having a voltage between 100 volts and 240 volts, depending on the system. In the United States, the low voltage section typically is about 120 volts (120V). The sections of the power distribution system that provide the power to the low voltage sections are referred to as the medium voltage. (MV) sections. The voltage of the MV section is in the range of 1,000 Volts to 100,000 volts and typically 8.66 kilo volts (kV) to neutral (15 kV between phase conductors). The transition from the MV section to the LV section of the power distribution system typically is accomplished with a distribution transformer, which converts the higher voltage of the MV section to the lower voltage of the LV section.
Power system transformers are one obstacle to using MV or LV power distribution lines for data communication. Transformers designed for conversion of voltages at power frequencies (i.e. 50 or 60 Hz) present complex and often undesirable series and shunt impedances that can be detrimental to data signal frequencies useful for data communication. As such, power distribution communication systems face the challenge of passing the data signals around (or sometimes through) the distribution transformers.
To bypass the distribution transformer, the bypassing system needs a method of coupling data to and from the medium voltage power line. Similarly, coupling data signals to and from the medium voltage cable at a repeater and backhaul location (a location where data signals are coupled on and off the power distribution communications system) requires the same or similar coupling means. As discussed, medium voltage power lines can operate from about 1000 V to about 100 kV, and often carry high amperage. Consequently, coupling to a medium voltage power line gives rise to safety concerns for the user installing the coupling device.
The coupling device should be designed to provide safe and reliable communication of data signals with a medium voltage power line—carrying both low and high current—in all outdoor environments such as extreme heat, cold, humidity, rain, wind, high shock, and high vibration. Also, coupling around the transformer raises concern that dangerous MV voltage levels may be provided to the customer premises on the data line, which the coupling device should prevent. In addition, a coupling device should be designed so that it does not significantly compromise the signal-to-noise ratio or data transfer rate and facilitates bidirectional communication. In addition, the coupling device (or coupler as referred to herein) should enable the transmission and reception of broadband radio frequency (RF) signals used for data transmission in MV cables.
Many couplers that have been designed prior to this invention have relied on direct contact with the MV power line, which typically carries a phase-to-phase 15 kV, 60 Hertz power transmission. The phase-to-earth ground voltage of the 15 kV system is 8.66 kV. As a consequence, the electronics and power supplies associated with the couplers have to be built to isolate the 8.66 kV potential from earth ground. Various embodiments of the coupler of the present invention may provide many of the above features and overcome the disadvantages of the prior art.